The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.
Electronic devices typically of several discrete integrated circuit packages on a single circuit board or printed circuit board (PCB). The computing power of these packages is rarely limited by their functional size within these devices but rather their total power consumption and heat generated. Smart phone devices use passive or conductive cooling within their systems, laptops use a combination of miniaturised conductive, phase change and fan forced cooling, and desktop computers use large fan forced and phase change cooling techniques to increase cooling efficiency. The smaller the device the greater the need for passive high speed conductive cooling.
A further use for PCBs is in Light Emitting Diode (LED) lamps. LED lamps are lamps or lights that have been assembled from an array of one or more LEDs. LED lamps have a lifespan and electrical efficiency that is several times better than incandescent lamps, and significantly better than most fluorescent lamps. This has seen LED lamps begin to replace incandescent lamps and fluorescent lamps in both commercial and residential applications. During this replacement period, LED lights have been made from LED lamps with standard light bulb connections and shapes (such as an Edison screw base or GU10 bayonet fitting) and are made compatible with the voltage supplied to the sockets. As the need for compatibility with existing fittings diminishes, newer fittings designed for LED lamps are emerging.
Despite the drastic improvement of LED lamps over conventional incandescent lamps and fluorescent lamps, there are still several limitations to LED lamps which must be addressed before they fully replace conventional lighting.
The major limitation of LED lamps is that LED efficiency and life span drop at higher temperatures. Most of the electricity in an LED is lost as heat rather than being transformed into light (about 70% heat and 30% light). If this heat is not removed the LEDs run at a high temperature, which not only lowers their efficiency, but also makes the LEDs less reliable than they might otherwise be. This therefore limits the power that can be used in LED lamps that are used to physically replace existing filament and compact fluorescent types. Accordingly, the management of heat in LED lamps, especially those that use high-power LEDs is essential.
One method of management of the heat In LED lamps is through the use of a metal core printed circuit board (MCPCB). In MCPCBs, the base material for the PCB is a thermally conductive metal, as opposed to cheaper boards constructed from insulating materials. Between the LED and the metal core there is provided a thermally conductive dielectric layer which acts as a thermal bridge between the LED and the metal core. A conventional heat sink may then be utilised to dissipate the heat transferred to the metal core. One problem associated with MCPCBs relates to ineffective heat distribution, which results in heat spots to form in certain areas of the board. The temperature differential between these heat spots and the remainder of the PCB can result in buckling and separation of the layers and improper heat transfer.
The heat sinks themselves also have limitations which are mainly related to the size restriction that comes with commercial and residential LED lamp installations. Whilst the spatial limitation can be improved by increasing the complexity of the heat sink and/or using special alloys in construction, this ultimately increases the cost of the LED lamp.
Another problem with LEDs that is particularly applicable to LED lamps is what is known as “efficiency droop”. This refers to the decrease in luminous efficacy of LEDs as the electric current increases past a certain point. Accordingly, luminance is usually increased by combining multiple LEDs in one LED lamp. The associated need for more LEDs has significantly increased the production costs of LED lamps.
Throughout this specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
Throughout the specification, unless the context requires otherwise, the term “evacuated core” or variations thereof will be understood to imply at least some level of evacuation of the core and is not to be limited to complete or entire evacuation. Further, the term “evacuation” implies a pressure lower than atmospheric pressure.